1. Field of the Invention
The present invention relates to a nonreciprocal circuit device such as an isolator and a circulator used at microwave bands, and relates to a mounting structure of the nonreciprocal circuit device and a communication apparatus having the nonreciprocal circuit device.
2. Description of the Related Art
Hitherto, a concentrated-constant-type isolator, for example, comprises a ferrite assembly having a plate-like ferrite with plural central conductors closely arranged thereto and intersecting with each other, a magnet accommodated in a case for applying a static magnetic field to the ferrite, and input-output terminals exposed or protruded outside the case.
FIGS. 13A to 15B show a method for pulling out the input-output terminals from the case of such a conventional isolator and a structure for mounting the isolator on a substrate of a communication apparatus or the like.
FIG. 13A is a perspective view of the isolator; FIG. 13B is a perspective view showing a state that the isolator is mounted on a printed circuit board of a communication apparatus. In this example, the input-output terminals of the isolator are respectively arranged on the substantially bottom surface of the isolator and the isolator is surface-mounted by soldering the input-output terminals of the isolator to connecting pads on the printed circuit board. A module circuit board 3 forming a circuit module is surface-mounted on the printed circuit board 2, and the circuit on the module circuit board 3 and the isolator are electrically connected together via an electrode pattern formed on the printed circuit board 2.
FIG. 14A is a side view of an isolator of another structure; FIG. 14B is a drawing showing a mounting structure thereof. In this example, input-output terminals are pulled out of intermediate portions of the part height of the isolator. As shown in FIG. 14B, when the bottom surface of the isolator body is a grounding conductor: the isolator body is fixed on an earth block (a common earth plate) with screws; the printed circuit board 2 having the same shaped-opening as the planar external shape of the isolator is arranged on the earth block; the isolator is fitted into the opening of the printed circuit board 2; the input-output terminals of the isolator are soldered to connecting pads on the printed circuit board 2.
FIG. 15A is a side view of still another isolator; FIG. 15B is a drawing showing a mounting structure thereof. This example is basically of the same structure as that shown in FIGS. 14A and 14B; however, input-output terminals are pulled out of the top surface of the isolator. This mounting structure may be adopted when the isolator thickness is relatively small.
By the way, in the conventional isolator and the mounting structure thereof shown in FIGS. 13A and 13B, the isolator and the preceding stage circuits are connected together via conductor patterns formed on the printed circuit board. Therefore, there have been the following problems.
1) The pattern for connecting the isolator and the preceding stage circuits together needs to be designed to have excellent matching for preventing a loss in signal delivery.
2) For the same reason, every time when changing any of the thickness and material of the printed circuit board, the shape of the conductor pattern, or the part arrangement of the isolator or the preceding stage circuit, as well as when changing electrical characteristics of the isolator or the preceding stage circuit, the patterns for connecting between the isolator and the preceding stage circuits have to be redesigned.
3) Even when the connecting pattern is designed to have most excellent matching, there will be certainly produced various kinds of losses such as losses due to radiation from the conductor pattern, dielectric losses of the printed circuit board, conductor losses of the conductor pattern, and losses due to reflection in an incomplete matching portion. Also, even when the above-mentioned design is completely performed, there are manufacturing scattered values of the connecting pattern in shape and size and the printed circuit board in thickness and permitivity, so that matching incompletion cannot be avoided due to the dispersion. Furthermore, when a dielectric material of the printed circuit board absorbs atmospheric moisture, dielectric losses in the connecting pattern may increase. Unnecessary radiation generated from the connecting pattern may also produce a malfunction by interference with other circuits on the printed circuit board. In particular, the place surely capable of producing the internal mutual interference is the pattern portion connecting between a heavy-duty isolator such as a signal transmission portion of radio-communication equipment such as a portable telephone and the preceding stage circuits, i.e., an electric power amplifier.
4) The connecting pattern is arranged on the printed circuit board between the isolator and the preceding stage circuit requiring an area for this position to occupy, so that the position becomes dead spots so as to have difficulty in miniaturizing the entire device.
In the isolator and the mounting structure thereof shown FIGS. 14A to 15B, there are the following problems other than the problems 1) to 4).
5) The printed circuit board is required to have the opening for fitting the isolator thereinto, so that unless the opening is simple shaped, a mold is needed causing increase in cost.
6) The earth block for connecting the grounding conductor on the bottom face of the isolator is needed on the bottom of the printed-circuit-board opening for fitting the isolator thereinto so as to have difficulty in miniaturization and reduction in weight of the entire apparatus such as a communication unit.
Accordingly, it is an object of the present invention to provide a nonreciprocal circuit device that solves various problems such as losses, unnecessary radiation, and the internal mutual interference, which are produced at a connecting point between the nonreciprocal circuit device and a circuit to be connected thereto, and also to provide a mounting structure of the nonreciprocal circuit device capable of promoting reduction in losses, size, and weight by facilitating matching with the circuit to be connected thereto.
A nonreciprocal circuit device according to the present invention comprises a case having a substantially rectangular parallelepiped shape, an input terminal group disposed in juxtaposition at a first height from a first side of a mounting surface of the case, and an output terminal group disposed in juxtaposition at a second height from a second side opposite to the first side of the mounting surface, wherein the first and the second height are different from each other. By this structure, the input terminal group or the output terminal group can be directly connected to connecting pads on a circuit board according to the height of the circuit board having circuits to be connected to the nonreciprocal circuit device.
The first height may be located at one of an intermediate height of the case and the top-face height of the case, and the second height may be substantially the same height as the bottom surface of the case. By this structure, the output terminal group is directly connected to a printed circuit board for mounting the nonreciprocal circuit device, and the input terminal group can be directly connected to connecting pads on the top surface of a module circuit board of preceding stage circuits to be mounted on the printed circuit board.
The height of the input terminal group may be determined by according to the thickness of the module circuit board forming the preceding stage circuits, so that the input terminal group of the nonreciprocal circuit device and the connecting pads of the module circuit board are of equal height in a state that the module circuit board and the nonreciprocal circuit device are mounted on the printed circuit board, thereby eliminating dead spots and reducing the thickness of the entire device.
The input and output terminal groups may include hot terminals and ground terminals, respectively. The width or thickness of at least one terminal of the input terminal group may be increased larger than that of any terminal of the output terminal group, so that the strength of the input terminal group located in a position separated from the top surface of the printed circuit board, and at which a stress is liable to concentrate, is increased, thereby the drop-proof strength of the communication unit can be improved.
The number of ground terminals of the input terminal group may be plural, so that the connecting strength of the input terminal group is increased and grounding connection is secured, thereby mismatching in impedance and unnecessary radiation can be securely prevented.
The input terminal group may be formed on the bottom surface of an insulator plate, so that the strength of the input terminal group and the drop-proof strength are improved.
The impedance of the input terminal group may be within the range of 3 xcexa9 to 30 xcexa9. When a preceding stage circuit of the nonreciprocal circuit device is a power-amplifying circuit for transmitting signals, it may be intended to achieve the overall efficiency higher compared with the case where the impedance is 50 xcexa9 by making the output impedance from 3 xcexa9 to 30 xcexa9. Even when connecting to the preceding stage circuit with such low impedance, the impedance matching can be easily performed by directly connecting the input terminal group of the isolator adjusted to have the matching in advance to the preceding stage circuit without using a connecting pattern formed on the printed circuit board. When circuits both having the low impedance are connected together, losses due to the resistance in series of the connecting pattern and the wiring are increased; however, the losses are negligible when the impedance matching is performed without using the connecting pattern on the printed circuit board.
In the nonreciprocal circuit device according to the present invention, the input terminal group may be weldable to connecting pads on the module circuit board. When the nonreciprocal circuit device and the module circuit board are welded together in advance by welding the input terminal group of the nonreciprocal circuit device to the connecting pads on the module circuit board, the connecting strength between both members is increased, so that the connecting portion of both members can be prevented from breaking apart due to heat of reflowing solder when soldering to the printed circuit board.
The input terminal group may be made of Ni, or a Ni-alloy, for example. Thereby, the welding strength is further increased, so that laser output power required for laser welding or a welding current required for resistance welding is reduced, thereby reducing equipment cost and electricity consumption during manufacturing.
In the nonreciprocal circuit device according to the present invention, a film made of Sn, a Sn-alloy, or solder may be formed on the input terminal group. Thereby, solderability and the connecting strength during soldering are improved. When flux is coated thereon, the connection to the module circuit board can be performed only by re-melting of the film, i.e., without solder-coating again.
In the nonreciprocal circuit device according to the present invention, a metallic member forming a case of the nonreciprocal circuit device or the ground terminals integrated with the metallic member may be connected to a shield member on the module circuit board for connecting to the input terminal group or the output terminal group. By this structure, the connecting strength between the nonreciprocal circuit device and the module circuit board is further improved. When both the members in a state connected together are mounted on the printed circuit board, the strength before mounting on the printed circuit board can be sufficiently increased. Furthermore, the nonreciprocal circuit device becomes continuous with the shield member on the module circuit board, so that the entire shielding effect increases.
In the nonreciprocal circuit device according to the present invention, a metallic material forming the case or a part of the magnetic circuit integrated with the case may be connected to a ground portion on the module circuit board for connecting to the input terminal group or the output terminal group, and the metallic material is allowed to serve as the case in the module circuit board side or as the shield member. By this structure, the connecting portion between the case of the nonreciprocal circuit device and the case to be arranged in the module circuit board side is avoided to be a weak point in the mechanical strength, i.e., in the stiffness. Also, a problem can be solved, in which the connecting portion between both the cases has a large electrical resistance, i.e., unnecessary impedance in series, thereby deteriorating the stability in the earth potential, so that the operation of the nonreciprocal circuit device integrated with the module circuit board becomes unstable.
In a mounting structure of a nonreciprocal circuit device according to the present invention, a nonreciprocal circuit device having any one of structures described above and a module circuit board are mounted on predetermined positions on a printed circuit board, and the input terminal group of the nonreciprocal circuit device is connected to first connecting pads on the module circuit board while the output terminal group of the nonreciprocal circuit device is connected to second connecting pads on the printed circuit board.